Conventionally, illumination apparatuses having a dimming function have been widely used. For example, an illumination apparatus using an incandescent bulb is dimmed by varying magnitude of current flowing through a filament that is a light source. By the way, when the incandescent bulb is dimmed from the dark state to the bright state, a luminescent color of the incandescent bulb varies from the orange color to the white color. This is because the luminescent color of the incandescent bulb varies depending on temperature and so on of the filament, and as the temperature of the filament decreases, color temperature of light emitted from the incandescent bulb decreases. Note that the temperature of the filament varies depending on magnitude of the current flowing through the filament.
On the other hand, there have recently been widespread, as alternatives to incandescent bulbs, illumination apparatuses using a light-emitting module having semiconductor light-emitting elements such as LEDs. Generally, a luminescent color of LED chips does not vary depending on magnitude of current flowing therethrough. This is because the luminescent color of the LED chips depends, not on the magnitude of the current, but on the band gap of semiconductor materials of the LED chips. For this reason, in the case where a lamp using LEDs as a light source (hereinafter, referred to simply as LED lamp) is used as an alternative to a incandescent bulb for an illumination apparatus having the dimming function, a user might feel discomfort about a luminescent color of the LED lamp during dimming.
By the way, Patent Literature 1 has proposed an LED module whose luminescent color is variable. In an LED module 901 as shown in FIG. 17, red LEDs 921a, 921b, 921c, 921d, 921e, and 921f (hereinafter, referred to collectively as red LEDs 921) parallel-connected to white LEDs 922a, 922b, 922c, and 922d (hereinafter, referred to collectively as white LEDs 922). Also, the white LEDs 922 are series-connected to a bipolar transistor 924. A base terminal of the bipolar transistor 924 is connected to a variable voltage source 927 via a base resistor 925. Also, a collector terminal of the bipolar transistor 924 is connected to an anode terminal of the white LED 922d. Furthermore, an emitter terminal of the bipolar transistor 924 is connected to a resistor element 926.
The LED module 901 is connected to a variable current source 933. AC power supplied from an AC power source 931 is AC/DC converted by an AC/DC converter 932, and DC power is supplied to a variable current source 933. As a result, the LED module 901 receives current supplied from the variable current source 933.
In the LED module 901, magnitude of base current of the bipolar transistor 924 varies in accordance with variation of magnitude of base-emitter voltage of the bipolar transistor 924. Here, as the magnitude of the base current increases, the magnitude of collector current of the bipolar transistor 924 increases. As a result, magnitude of current flowing through the white LEDs 922 increases. By increasing a magnitude ratio of the current flowing through the white LEDs 922 to current flowing through the red LEDs 921, a luminescent color of the LED module 901 approaches the orange color. Note that in order to vary the luminescent color of the LED module 901 in accordance with dimming, it is necessary to appropriately designate the base-emitter voltage of the bipolar transistor 924.